Molten iron for Roman road repairs?

[JHCC]

It seems that the Romans may have melted iron-rich slag and poured it into cracks to repair the streets of Pompeii. 

https://www.livescience.com/65479-ancient-romans-used-molten-iron-street-repair.html

[Irondragon Forge ClayWorks]

That's pretty amazing.

[Frosty]

I saw that on Livescience too. I sure wish they'd presented better pictures, I can't afford to subscribe to the publications and read the real articles. 

What really has me curious is why iron was in such supply in Pompeii they could afford to use it for road repair. Concrete was in common use in the Roman empire and iron slag would make a fine wear resistant aggregate. The Romans were a practical people well till the end that is so I have to wonder why hauling ladles of molten iron around the streets was more practical than mixing concrete on the spot.

Frosty The Lucky.

[JHCC]

That’s a fair question, and it led me to wonder if there was any significant iron smelting going on in the area that would have produced significant quantities of slag. 

It’s worth noting that the Romans did a lot with molten metal fastenings. Many of their masonry constructions were held together not just with mortar (which is great under compression) but also with iron ties held in place with pours of molten lead (better under tension). 

[Frosty]

Raising interesting questions is what I like about Livescience though some of their links and opinions are pretty dicey.  

The leaded in iron locking keys is why so many Roman structures are still standing. While working in the materials lab I had to test leaded anchors to determine if it was worth replacing them with epoxy or cylcap cements. Cylcap is a crazy sticky clay and sulfur mixture that melts at a relatively low temp and neither expands nor contracts as it cools. 

The more we learn about Roman architecture  and science the less surprised I am when something new is learned.  If I recall correctly they used bronze for rebar in concrete because iron rusts quickly in concrete and breaks it up. I think their opinion of what fast means says a lot about how far ahead they thought. 

Frosty The Lucky.